A red Fishing tome is a experience reward from the minigame, Temple Trekking. You can get one by taking one of the hard followers to Paterdomus or to Burgh de Rott. At the end, you will get a Reward token (red) which you can exchange by clicking on the first option, Claim-reward. The Fishing tome grants Fishing experience once read, and the blue version will give 4015-5005 Fishing experience.